1. Field of the Invention
The present invention relates to a polyolefin resin molding composite and, more specifically, to a polyolefin resin molding composite using thermoplastic expanded resin particles.
2. Description of the Related Art
With respect to a vehicular interior decoration member, there has hitherto been a member comprising an intervening foam layer between a base member of a solid resin and a surface layer, thereby attaching soft touch to the member to make it luxurious. The process for producing such a vehicular interior decoration member is disclosed in a patent publication (U.S. Pat. No. 2,500,645).
The process for producing a vehicular interior decoration member disclosed in the above patent publication comprises placing a sheet for a surface layer made of polypropylene on one mold, and on the other mold, placing a base member made of a solid resin that is made of polypropylene and contains fillers, filling expanded resin particles made of polypropylene into the space between the sheet for a surface layer and the base member, thereby fusion bonded particles one another to form a foam layer. This process provides such a mold.
However, the hitherto mold producing technique needs high temperature or high pressure steam heating when expanded resin particles are fusion bonded. This leads to a drawback that surface quality of a surface layer is deteriorated by heat when heating. Therefore there is another drawback that when a design as an interior decoration member is formed on the surface of a surface layer, the design becomes difficult to predominate. There is also another problem that if molding is carried out at a low temperature, fusion bonded between expanded resin particles is deteriorated and adhesion of the surface layer and the foam layer and of the foam layer and the base member are also deteriorated.
Furthermore, the above mentioned hitherto molding composite producing technique requires to heat for a long time by a high temperature steam in order to increase adhesiveness between a sheet for a surface layer and expanded resin particles. Because of this condition, when fusion bonded by heating is conducted, much moisture in a gas state infiltrates into spaces between expanded resin particles or particles themselves. If cooling is carried out in this condition, moisture condenses from the gas state to the liquid state, thereby causing great volume shrinkage.
On this account, pressure in the spaces between expanded resin particles or in the particles themselves reduces, thereby causing shrinkage or deformation of an expanded mold made of these particles. This leads to a problem that shape stability becomes worse, that it is hard to obtain a mold fitted exactly in a mold, and that surface appearance of a surface layer is bad. Moreover, in respect of an expanded mold, it is needed that expanded resin particles are sufficiently fusion bonded one another, thereby achieving a high mechanical strength.
The present inventors have investigated wholeheartedly these problems of a hitherto molding composite having a foam layer, thereby developing an excellent molding technique that a foam layer can be molded at such a temperature as not to deteriorate surface quality of a surface layer, and a technique excellent in adhesiveness of a foam layer and a surface layer or/and a base member, and achieving a resin molding composite.
The present invention is a polyolefin resin molding composite, and is constituted as follows to overcome the above mentioned technical problems. That is, the present invention is characterized by a polyolefin resin molding composite comprising a surface layer and a foam layer, or a surface layer, a foam layer, and a base member, wherein the foam layer comprises a foam layer produced by fusion bonding thermoplastic expanded resin particles one another by molding, where the thermoplastic expanded resin particles comprises a core that is made of a crystalline thermoplastic resin and is in an expanded state and a polyethylene resin coat covering the core, and the surface layer comprises a thermoplastic synthetic resin having a melting point of 5xc2x0 C. or more higher than a melting point of polyethylene resin constituting the coat of the particles.
The polyolefin resin molding composite of the present invention is consisted of the above mentioned required elements, and is satisfactorily accomplished in the case that the elements are specifically the following elements. One of the specific elements is characterized by that thermoplastic synthetic resin constituting the surface layer is a polyolefin resin. It is also preferable that compressive hardness of the foam layer is 0.05 to 0.7 MPa. Moreover, it is also preferable that void fraction of the foam layer is 1 to 40%.